Onion Valley, in the Eastern Sierra, is perhaps the most difficult climb in California and among the most spectacular in the world. It is steeper and longer than both the Tourmalet and the Galibier, two iconic climbs of the Tour de France. Enjoy the first few miles. They are about the only break you will get on this hill. The grade ramps up as you ascend, with the last ten miles averaging over 8 percent. There are lots of switchbacks, and a dramatic section of them about halfway up the climb is the highlight, as it offers huge exposure and views over the Owens Valley. The torturously twisting descent is hair-raising and perhaps the top overall downhill in the United States.

Summerson says: “Probably my favorite climb of all. It’s just stupendous! Onion Valley is one of those rare hills where you may rue the end of climbing.”

Logistics: From Highway 395 in Independence, California, turn west on Market Street. The climb starts 0.4 miles down this road (which becomes Onion Valley Road) at the cattle guard. There’s not too much in Independence, but the town of Bishop, 40-some miles north, is the jumping off point for lots of adventuring (Owen’s River Gorge, Buttermilk Boulders). Try the Chalfant House (from $90 a night), an 1898 home that’s been fully restored into a B&B.